1. Field of the Invention
This invention relates to a configurable umbrella which can be converted into different shapes having a rib assembly which includes a rigid portion and a flexible portion that provides non-uniform flex strength of the ribs.
2. Description of the Related Art
A conventional umbrella typically has a cloth covered, dome shaped canopy that is symmetrical to a central pole and is supported by ribs that are secured to the pole and radiate outward. The ribs are evenly spaced around the pole and their cantilevered outer portions are equally flexed. Each rib is exactly the same and all are operated in unison via a single slide on the pole. In operation the umbrella is opened to its functional configuration or closed for storage by collapsing the ribs against the pole.
Conventional ribs of an umbrella have the same flex strength since each rib is formed of the same material and construction. The cantilevered portion of a conventional rib is composed of one material and is constructed with uniform thickness throughout its length. Thus, the flex strength of any rib is uniform throughout its cantilevered length. Accordingly, all conventional ribs share a common curvature profile when pressure is applied along the rib length. The curvature rate peaks in the first third of the distance from the fixed end to the free end, declines almost to zero in the middle third, and the third nearest the free end is essentially straight.
An open conventional canopy holds its intended shape since each rib of the umbrella is flexed in the same manner, the canopy is symmetrical to the pole, the cantilevered portions are the same length and the canopy cover is contoured to fit the flexed ribs. When these conditions are met the restraining force of the fabric and the restoring force of the flexed ribs can be sufficiently in equilibrium throughout the canopy to hold its shape. Conventional umbrellas have the shortcoming that if any of the above-described conditions are not met the ribs will not fit the fabric contour because they will seek equilibrium outside their intended positions, and the canopy will not hold its shape.
U.S. Pat. No. 5,505,221 describes a modification to the typical dome configuration of an umbrella with off-center support. The umbrella is symmetrical along a central vertical plane rather than the pole. Ribs of differing lengths are used to form a canopy having an elongated dome. A similarly shaped umbrella is described in Italian patent number 0372882. U.S. Pat. No. 4,838,290 describes a hat shaped umbrella with asymmetric properties, having cantilevered rib portions of differing lengths.
U.S. Pat. Nos. 5,307,827 and 5,355,903 issued to one of the inventors of this disclosure describe a dual function asymmetric umbrella. The primary embodiment of these patents is an umbrella in which the configuration can be altered to form a shade for auto windshield interiors. Ribs are unevenly spaced around the pole having cantilevered portions of differing lengths. The canopy has a flattened center in order to fit against a windshield and does not have a conventional dome shape.
In the closed position all ribs of the dual function umbrella are folded against a collapsed pole. From the closed position the umbrella can be opened and latched in either of two positions, each producing a different canopy configuration. In one open position, some of the ribs are partially extended and some are fully extended causing the canopy configuration to be approximately rectangular so it can be placed against the inner surface of a vehicle windshield as a shade. In the other open position all ribs are fully extended to produce an oval canopy to function as a conventional rain umbrella. The ribs that can be either partially or fully extended are referred to as "multiple position ribs." Their outer portion can be extended or folded by moving two slides on the pole. The other ribs are conventionally constructed and operated. The multiple position rib inner portion supports and controls the outer flexible portion using a push bar that runs the length of a girder from the pole to a piston housed at the other end of the girder. The piston is connected to the rib by a hinge. The above-described dual function umbrella has several shortcomings such as: the multiple position rib has a limited range of motion; the multiple position rib lacks the rigidity to hold a fully extended rib firmly in place; the use of multiple position ribs and conventional ribs in the same umbrella causes canopy surface unevenness; push bars used in the multiple position rib are vulnerable to damage; when the umbrella is to be used as a car shade four ribs are fully opened to extend the canopy horizontally which makes it difficult to place against the windshield if the entire upper surface of the dashboard is not flat; and the rib construction poses a sizing problem for the car shade umbrella in that one size umbrella fits a limited number of vehicles and is either too large or too small for most windshields.
Conventional rib construction causes the rib tips of umbrellas to be inflexible and therefore hazardous when the canopy is being opened or is in use. It is well known that the rib tips can cause eye and other injuries. This disadvantage has always been considered inherent to umbrellas and inescapable.
It is desirable to provide an umbrella which can be varied in shape and provide improved stability, safety and reduced vulnerability to damage.